I know you can make 3D models be a fixed size (i.e. sized effectively by pixels rather than meters). I'm using that and it works great.
Is this possible with the regular 3D shapes, e.g. cones, spheres, etc.? Seems strange that you'd have to create a model file and load it in order to use that feature, in which case as far as I can tell you then lose the ability to color the 3D shape the way you want.